The ozone is a protective layer in the upper atmosphere, which helps absorb UltraViolet-B (UVB) from the sun. However, when greenhouse gases are released from ground level, they move up into the ozone layer and essentially damage this layer. Reductions in stratospheric ozone levels lead to higher levels of UVB reaching the Earth's surface. Consequently, laboratory and epidemiological studies demonstrate that UVB can cause nonmelanoma skin cancer and can also play a major role in the development of malignant melanoma. Holes in the ozone layer have been linked to increased cases of skin cancers for some time now, and according to a new study lead by University of California, Berkeley, chronic exposure to ground level ozone itself is now being linked to cardiovascular disease and even premature death.

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Ground level ozone is different from stratospheric ozone in the fact that at ground level, ozone is a major component of photochemical smog, which has a noticeable light brown color and results in reduced visibility. Not only is ground level ozone a powerful greenhouse gas, but it is a widespread air pollutant in many major cities.

The analysis, funded by the California Air Resources Board and published in the current issue of American Journal of Respiratory and Critical Care Medicine, also found a strong link between nitrogen dioxide, a marker for traffic pollution, and increased risk of death from lung cancer.

Numerous studies have connected air pollution to a higher risk of mortality, but until now, the extent of the impact had been uncertain.

For the new paper, researchers developed individualized air pollution exposure estimates of more than 73,000 California residents. They used a combination of home addresses, government air monitors and statistical models to obtain monthly averaged values of exposure to ozone, nitrogen dioxide and fine particulate matter pollution. Researchers tracked mortality from 1982-2000 to link the deaths to air pollution exposure.

"Ozone has already been linked to respiratory problems, but this is the first study to show that it also increases the risk of death from ischemic heart disease, which accounts for more than 7 million deaths worldwide each year," said study lead author Michael Jerrett, professor and chair of environmental health sciences at UC Berkeley's School of Public Health. "Our findings will likely up the total deaths due to air pollution by hundreds of thousands per year in the next World Health Organization assessment."